Carn Euny is an archaeological site near Sancreed , on the Penwith peninsula in Cornwall, United Kingdom with considerable evidence of both Iron Age and post-Iron Age settlement. It is best known for the well-preserved state of the large fogou, an underground passageway, which is more than 65 feet (20 metres) long.

It is thought to be connected with the settlement at Chysauster.

The site was abandoned late in the Roman period.